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THE SKULL AS A WHOLE. 135 
tips of which are directed forward; and a corresponding pair of 
anterior clincid processes lie at the anterior end of the fossa, 
with the tips directed backward. The posterior, and also dorsal 
wall of the fossa, described as the dorsum sellae, leads by an 
abrupt curve backward on to the floor of the posterior cranial fossa, 
the sloping portion of the floor, or clivus, supporting in the natural 
condition the pons and medulla oblogata. Toward the anterior 
end of the middle cranial fossa, the lateral walls of the skull are 
greatly compressed, so that the anterior portion of the basicranium, 
especially the body of the anterior sphenoid, is largely ecxluded 
from the cranial cavity. The usually paired optic foramina are 
here confluent, there being a single aperture for the transmission 
of the optic nerves. The posterior ventral boundary of this aper- 
ture contains a broad groove, the sulcus chiasmatis, which lodges 
in the natural condition the optic chiasma. 
In the anterior cranial fossa the floor is largely formed by a 
perforated area, borne on the cribriform plate (lamina cribrosa) 
of the ethmoid bone, and serving for the transmission of the 
divided olfactory nerves. Its median portion projects slightly into 
the cranial fossa as a low ridge, the crista galli, which is interposed 
between the tips of the olfactory bulbs. 
In the ventrolateral portion of the cranial cavity may be found 
the internal openings of the foramina described above, namely, the 
superior orbital fissure, the foramen lacerum, the jugular foramen, 
and the hypoglossal canal. The superior orbital fissure is almost 
ventral in position to the foramen opticum, and is connected back- 
ward with the foramen lacerum by a broad groove, the sulcus 
sphenoidalis, which lodges in the natural condition the roots of 
the fifth nerve. This groove continues to the medial surface of the 
periotic bone, where it is bridged over by the tentorium cerebellt. 
On the lateral wall of the posterior cranial fossa, and 
enclosed by the compact, white, petrous portion of the peroitic 
bone, is a series of three apertures leading into its substance. 
One of these, much larger than the remaining two, is_ the 
parafloccular fossa (fossa parafloccularis). It lodges in the 
natural condition the flocculus, a small stalked appendage of the 
cerebellum. Ventral of this fossa, and also somewhat in front of it, 
a thin lodge of bone extends over an oval opening, the internal 
